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    <script>
        /*
           常量（const）：声明之后不允许改变
                          1.const不允许重新赋值
                          2.声明的时候必须初始化
                          3.const是块级作用域
                          4.

        */
       const PI = 3.14;
       console.log(PI);
    //    PI = 3.25;

       {
        const i = 1;
       }
       console.log(i);
    </script>
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